The increasing demand on fuel efficiency requires engines to provide higher output without increasing total piston displacement and/or weight. One effective way to achieve this is through forced induction systems to boost the intake pressures. More air and thus more fuel can be added to each cylinder. Consequently, more mechanical power is generated from each explosion in each cylinder.
There are two basic types of forced induction systems. One is referred to as supercharger and the other is referred to as turbocharger. The difference between the two systems is their source of energy. Turbochargers are powered by the mass-flow of exhaust gases driving a turbine; superchargers are powered mechanically by belt or chain drives from the engine crankshaft driving a turbine.
In general, superchargers offer a few advantages over turbochargers. The advantages include no turbo lag; they are easy and inexpensive to install; and there is no heat inertia effect in the exhaust system. This makes superchargers the most cost-effective way to increase engine power output.
Conventional superchargers are driven by the engine's crankshaft through a fixed gear ratio. The boost ratio increases with engine speed. At low engine speed, the boost ratio is low and insufficient to provide desired engine torque. There is a strong desire to develop a variable speed supercharger that is capable of delivering optimal boost ratios across the entire spectrum of engine speed, thereby providing additional engine torque even at low engine speeds